-- ======================================================================
-- Hell Lua Bus
-- 
-- Copyright 2012-2014 Hell-Prototypes
--
-- http://www.hellprototypes.com/
--
-- This is free software, licensed under the terms of the GNU General
-- Public License as published by the Free Software Foundation.
-- ======================================================================
module(..., package.seeall);

-- CRC table for the CRC-16. The poly is 0x8005 (x^16 + x^15 + x^2 + 1)
local crc16_table  = {
    0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
    0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
    0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
    0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
    0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
    0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
    0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
    0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
    0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
    0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
    0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
    0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
    0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
    0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
    0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
    0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
    0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
    0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
    0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
    0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
    0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
    0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
    0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
    0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
    0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
    0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
    0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
    0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
    0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
    0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
    0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
    0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040
}

function crc16(buffer, len)
	local crc = 0;
	local crc_h = 0;
	local buff_idx = 1;
	local tab_idx;

	while len > 0 do
		len = len - 1
		tab_idx = bit32.band(bit32.bxor(crc , buffer[buff_idx]), 0xFF) + 1
		buff_idx = buff_idx + 1
		crc_h = bit32.rshift(crc, 8)
		crc = bit32.bxor(crc_h , crc16_table[tab_idx])
	end

	return crc;
end


function crc16_ccitt(p_data, size, p_crc)
    local crc = (p_crc == nil) and 0xffff or p_crc;
    for i = 1, size do
        --crc  = (unsigned char)(crc >> 8) | (crc << 8);
		crc = bit32.bor(bit32.rshift(crc, 8), bit32.band(bit32.lshift(crc, 8), 0xFF00))
		--crc ^= p_data[i];
		crc = bit32.bxor(crc, p_data[i])
        --crc ^= (unsigned char)(crc & 0xff) >> 4;
		crc = bit32.bxor(crc, bit32.rshift(bit32.band(crc, 0xFF), 4))
        --crc ^= (crc << 8) << 4;
		crc = bit32.bxor(crc, bit32.band(bit32.lshift(crc, 12), 0xF000))
        --crc ^= ((crc & 0xff) << 4) << 1;
		crc = bit32.bxor(crc, bit32.lshift(bit32.band(crc, 0xFF),5))
    end

    return crc;
end


--CRC16              = 0xBB3D      /  47933
--CRC-CCITT (0xffff) = 0x29B1      /  10673
--[[
raw = {0x31,0x32,0x33,0x34,0x35,0x36,0x37,0x38,0x39} --CRC16 : 0xBB3D
print(string.format("CRC16 = 0x%04x", crc16(raw, 9)))
print(string.format("CRC16-CCIT 1 = 0x%04x", crc16_ccitt(raw, 9, 0xFFFF)))
print(string.format("CRC16-CCIT 2 = 0x%04x", crc16_ccitt(raw, 9, 0x0000)))
print(string.format("CRC16-CCIT 3 = 0x%04x", crc16_ccitt(raw, 9, 0x1d0f)))
--]]